Dust was blooming marvellous for harbour

By Deborah Smith SCIENCE EDITOR

6 October 2009 — 12:00am

THE thick blanket of red dust that settled on Sydney two weeks ago caused the harbour to bloom.

Nutrient-rich topsoil from the city's worst dust storm in about 70 years led to a tripling in the number of microscopic plants, or phytoplankton, in the upper layers of water, Sydney scientists have found.

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They also calculate this invisible explosion in photosynthetic life in the harbour and Tasman Sea would have soaked up an amount of carbon dioxide equivalent to a month's emissions from the Munmorah Power Station on the Central Coast.

Ian Jones, head of the University of Sydney's ocean technology group, said Sydney coastal waters were low in nutrients such as nitrogen and phosphate that phytoplankton required to grow. ''We're sitting in an ocean desert in Australia,'' he said.

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The results of the natural dust experiment were ''vindication'' for his team's controversial plans to nourish the ocean artificially with nitrogen-containing urea. He said this approach could not only help tackle climate change but also help feed the hungry or poor in countries such Morocco.

Phytoplankton growth increases fish production. ''If we continuously nourished a patch of water about 20 kilometres in diameter we could support poor artisan fisherfolk and we could raise their daily income from $1 to $2, while storing 10 million tonnes per year of carbon dioxide in the deep ocean,'' he said.

Like all plants, phytoplankton absorb this greenhouse gas from the environment, taking the carbon with them when they die and sink to the bottom.

Other scientists, however, have raised concerns about ocean fertilisation with nutrients such as iron. A recent report by the Royal Society in Britain concluded that, as a large-scale solution to climate change, it has ''a high potential for unintended and undesirable ecological side effects''.

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The Sydney team has regularly tested for chlorophyll at Chowder Bay, home of the Sydney Institute of Marine Science, and at a site 10 kilometres offshore, to determine phytoplankton levels and the impact of events such as heavy rain.

The massive dust storm was a fortuitous case of the ''world collaborating with scientists'', Professor Jones said. The results would boost their case for an initial experiment to spread 2.5 tonnes of nitrogen, in the form of urea, in the Tasman Sea, which would need government approval to go ahead, he said. ''Our tests would be perfectly safe in an environmental sense.''